The cochlear implant for severe to profound deafness is among the most successful neural prostheses. However, the anatomic and physiologic substrates that are responsible for the considerable variability of an implant in a given individual as measured by open set speech discrimination are unknown. Identification of these variables would allow better methods for preoperative counseling, patient selection, and improvement in electrode design and speech processing. The research plan uses computer modeling to identify peripheral anatomic and physiologic factors that influence performance of cochlear implants in a growing collection of temporal bones from patients who had undergone cochlear implantation during life and whose speech recognition scores are known. In addition, more recently it has been demonstrated that under certain conditions residual auditory hearing may be preserved with performance of a cochlear implant and furthermore that combined electrical and acoustical stimulation (EAS) may be superior to electrical stimulation alone. However, the variables that limit preservation of acoustic hearing in an implanted ear are unknown. The research plan envisions use of our temporal bone collection of implanted cases and normal anatomy to better predict the ideal cochleostomy site to limit cochlear damage and in the implanted bones to fully evaluate cochlear pathology induced by the implantation process. Successful achievement of the specific aims of the project will improve patient selection, broaden the patient population who may benefit from cochlear implantation, and improve the performance of implant users as measured by open set speech discrimination.